This week, Chicago Mayor Rahm Emanuel negotiated a deal with local teacher unions designed to improve school operations for more than 350,000 children. While the new contract is far from perfect, several items stand out as positive steps forward. First, students may be given more opportunity to learn through longer school days across any given year. As long as most students have access to an effective teacher with this additional time, one would expect more productivity to result.

Ultimately, the measure of any teacher has to come by assessing how well they teach their students, year after year. Central to evaluating teacher quality and effectiveness must be periodic and regular student achievement tests and scoring. It is unfortunate that many public sector unions that claim to represent a teacher’s best interests are reluctant to embrace value-added models of student advancement.

In the recent case of Chicago, the teachers union resisted the notion that 30 percent of their evaluation should be based on student performance. It is hard to imagine that union-employer debates in any other industry would be resolved with such low expectations of performance. Government may be at its worst when it confuses spending and investment as former hedge fund manager Andy Kessler pointed out this week in the Wall Street Journal. When hiring decisions and salary increases are not based on student performance, schools are virtually certain to be misallocating capital. If these associated costs only led to set backs in school operations and management, there would be reason enough to change the ill-conceived hiring policies. However, the true costs of ineffective teachers inside public school systems are much larger than this since schools supply America with its workforce of tomorrow.

Today, the Institute for a Competitive Workforce is hosting a conference on how America is addressing the skills gap crisis. Employers, educators and workforce development organizations from around the country are meeting to discuss how to realign educator outputs to labor market needs and improve our workforce’s ability to compete in a global economy. Workforce demands are increasing at the same time that productivity inside the classroom becomes increasingly important. In today’s economy, educators will need to do more with fewer resources. Clearly, the need for the best, most effective teachers inside our classrooms is more critical than ever.

Peer-reviewed studies by Eric Hanushek of Stanford University have considered the effect of eliminating the worst teachers by replacing these teachers with average teachers. Eliminating the least effective five to eight percent of teachers would bring up student achievement by very substantial standards when scored by international tests. This is why seniority-based layoffs, such as those imposed in Chicago, are so harmful to society at large. By making it difficult to dedicate our best teachers to America’s education challenges, union work rules are locking in higher prices with lesser results.

Unless your children are among those classes stuck with a poor performing teacher, you may be inclined to neglect this problem by hoping for better over the next school year. However, the compounding costs from an incomplete education shows up in lost wages for employees, remedial training among colleges and universities, and even our aggregate growth rates for the national economy. By one account from Hanushek and Woessman, the present value of added GDP from replacing our least effective teachers is worth $70 trillion (compared with a US GDP of $15 trillion in 2011).

It should not take a strident Mayor to rival a high-profile teacher strike in order to replace non-performing teachers. Until America’s best and brightest teachers stand up to their own unions holding them back, I am glad that the kids have Mayor Rahm Emanuel.